1. Field of the Invention
The present invention relates to a planographic printing plate precursor, more specifically, a negative or positive type planographic printing plate precursor which can be directly made a printing plate by scanning exposure based on digital signals, is superior in printing durability, and generates no stains in a non-image portion.
2. Description of the Related Art
In recent years, with development in solid lasers or semiconductor lasers having a light emission wavelength within a near infrared range or infrared ray range, more attention has been paid to systems using such infrared ray lasers as systems in which a printing plate is made up directly from digital data stored in a computer.
As the material for a positive type planographic printing plate for direct plate-making with infrared rays, there is disclosed, for example, a material obtained by adding a substance which absorbs light to generate heat and a positive type photosensitive compound such as a quinine diazide compound to a resin soluble in aqueous alkali solution (see Japanese Patent Application Laid-Open (JP-A) No. 7-285275). In an image portion of a precursor for such a positive type planographic printing plate, the positive type photosensitive compound functions as a dissolution inhibitor which substantially decreases the solubility of the resin soluble in aqueous alkali solution. In a non-image portion thereof the compound is decomposed by heat to lose the dissolution inhibiting capability. As a result, the compound and the resin soluble in aqueous alkali solution, in the non-image portion, is removed by development, to form an image.
It is known that onium salts or compounds which can make hydrogen bond nets having a low alkali solubility have an effect of suppressing the dissolution of the alkali-soluble polymer in the alkali solution. Regarding an image forming material which can be exposed with an infrared ray laser, it is that a composition in which a cationic infrared ray absorbing dye is used as the agent for suppressing the dissolution of the alkali soluble polymer exhibits positive type effect (see WO No. 97/39894 pamphlet). This positive type effect is the effect that the infrared ray absorbing dye absorbs a laser ray and due to the generated heat, the suppression of the dissolution of the polymer film in the laser-radiated portion disappears, thereby an image is formed.
An example of a negative type image forming method is a recording method in which using an acid generated by light or heat as a catalyst, condensation crosslinking reaction is caused by heating treatment after exposure, the exposed portion of a recording layer is cured to form an image portion. And a technique utilizing such an acid catalyst crosslinking type recording layer is known (see JP-A No. 7-271029). Another example is a recording method in which using radicals generated by light or heat as an initiator, a polymerization reaction is caused and the exposed portion of a recording layer is cured to form an image portion. As a printing plate having such a light or heat polymerization type recording layer, a technique in which a photopolymerizable or heat polymerizable composition is used as a recording layer is known (see, for example, JP-A Nos. 8-108621 and 9-34110).
About supports used in such planographic printing plates, hitherto research has been actively made for making the surface of the supports hydrophilic in order to prevent stains on non-image portions. For example, in the case that a metal support such as an aluminum plate is used as a substrate, various techniques are suggested, examples of which include an anode-oxidized aluminum substrate, and an anode-oxidized aluminum substrate further treated with silicate to make the hydrophilicity higher.
However, it cannot be necessarily the case that various treatments for improving the hydrophilicity are superior in affinity to recording layers. And there has been a problem that in some cases, the adhesion between the support and the recording layer formed thereon is impaired so that the recording layer is peeled under strict recording conditions and sufficient printing durability cannot be obtained.
Thus, methods are suggested in which at least one layer selected from various intermediate layers is formed between the support and the recording layer, in order to improve the contact characteristics between the recording layer and the support surface to which hydrophilicity has been imparted. When a material having a functional group superior in affinity to the resin material which constitutes the recording layer or the support surface is used for the intermediate layer, the contact characteristics in an image portions is improved and a sufficient printing durability can be obtained. However, in a non-image portion, the recording layer is not quickly removed at the development, and remains as a film on the support surface to cause a problem that adhesion of ink onto the remaining film causes stains in the non-image portion.
It has been therefore desired to develop a support which has superior surface hydrophilicity thereof and gives both superior contact characteristics to a recording layer in an image portion and superior removability of the recording layer in a non-image portion.
In order to solve the above-mentioned various problems, a technique of forming an intermediate layer made of a water-soluble polymer such as polyacrylic acid or carboxymethylhydroxyethylcellulose (see U.S. Pat. No. 3,136,636) is suggested. However, this technique does not give a satisfactory printing durability. Also, a technique of forming an intermediate layer made of a tertiary ammonium compound such as poly(dimethyldiallylammonum chloride) is suggested (see U.S. Pat. No. 4,483,913). However, this technique is also not satisfactory since stains are generated in a non-image portion thereof.
Furthermore, the inventors suggested a planographic printing plate having an intermediate layer containing a polymer compound comprising a specific structural unit such as p-vinyl benzoate (JP-A No. 10-69092). The inventors also suggested a planographic printing plate precursor having an intermediate layer containing a polymer (random polymer) comprising a monomer having an acid group and a monomer having an onium group (JP-A No. 2000-108538). These techniques give certain degree of improvements. However, it is desired in the present situation to improve the contact characteristics between a support and a recording layer, make the printing durability of a planographic printing plate precursor higher, and suppress the generation of stains effectively in non-image portions of the plate.